Vertical kiln

ABSTRACT

Trays are provided with identical vertical spacers which enable the trays to be stacked on top of each other in a centered way, with a suitable or appropriate spacing between them, and enable the various adjacent stacks of trays to be raised and lowered in steps, by an elevating and lowering system which acts only on the bottom tray of each stack. The sides of the stacks of trays of the kiln are thus free and can be engaged by conveyors for the translation of the trays between the stacks, both in a normal operating cycle and in a short operating cycle. However, the lower translation conveyors, which transfer the trays from the stack with an unloading station to that with a loading station, are positioned in the conventional way, i.e., under the stacks of trays and transversely with respect to the trays.

FIELD OF THE INVENTION

The invention relates to vertical kilns or dryers, used for dryingproducts such as panels or articles of timber or other material, forexample after painting, coloring, impregnation or other types ofoperation. Equipment of this type contains, within a parallelepipedalheating chamber, two or more adjacent stacks of horizontal trays, whichare carried by an elevating and lowering system and by a translatingdevice along a zig-zag path which usually starts at the base of thefirst stack with an ascending movement, at the point where the trays areloaded with the articles to be dried, and which terminates at the baseof the last stack with a descending movement, at the point where thedried articles are unloaded from the trays. A final translating devicethen transfer the empty trays directly from the lower part of the laststack to the lower part of the first stack, thus forming the path of thetrays into a closed loop.

To gain a clearer idea of the problems encountered in vertical kilns ofthe known type, reference is made to FIGS. 1 and 2 which show,schematically and in a theoretical way, a known kiln with two stacks oftrays, seen from the side and from the front of one of the stacksrespectively. The trays V of the stacks C1 and C2 are, for example, ofrectangular shape and have their short sides resting on brackets Mcarried by opposite vertical pairs of chain conveyors T1 and T2, whichare synchronized with each other and provided with an intermittent andopposing motion, to elevate the trays in the stack C1 and lower those inthe stack C2. The brackets of the conveyors T1 and T2 are alignedhorizontally with each other, and thus when a tray reaches the top ofthe stack C1 it can be transferred to the top of the stack C2 by meansof horizontal chain conveyors T3, parallel to the path of translation,which have teeth D which push the long side of the tray and transfer itfrom the brackets of T1 to the coplanar brackets of T2.

The tray which cyclically reaches the bottom of the stack C2 first hasthe dried articles unloaded from it at a station K2 and is then placedon a horizontal chain conveyor T4 which transfers the empty tray at thecorrect time from C2 to C1, where means operate at the station K1 toload new articles for drying on to the empty tray. The stages oftransfer of the trays between the two stacks take place at the same timeas the stages of loading and unloading other trays at the stations K1and K2.

In a known kiln of this type or of a similar type, the followingdrawbacks are encountered. The presence of the chains of the conveyorsT1 and T2 throughout the height of the stacks C1 and C2, and especiallythe presence of the conveyors T3 located transversely and above thetrays of C1 and C2, can cause dirt to fall on the articles contained inthe trays, thus inevitably leading to the rejection of products.

The whole of the weight of the trays contained in the stacks C1 and C2is discharged on to the upper return shafts of the conveyors T1 and T2,and these shafts must therefore be supported by a frame which hassuitable load-bearing characteristics, and is therefore relativelyheavy, bulky and expensive.

As shown in FIG. 2, the conveyors T1 and T2 have a considerable depth,and make it necessary to provide means of circulating the hot drying airat a considerable distance from the ends of the trays located in thestacks C1 and C2, with markedly adverse effects on the functionality ofthese means.

The chains which form the elevating and lowering conveyors T1, T2 aremechanisms which, although very reliable from the technological point ofview, are expensive and require periodic maintenance.

When the known conveyors T1 and T2 for elevating and lowering the traysare used, it is very difficult to apply the method of short-cyclemovement of the trays, described in Italian patent application No. BO99A 000089 in the name of the applicant, to which reference willgenerally be made, according to which the trays are elevated by at leastone step from the loading station and then the trays are translated andlowered directly to the unloading station from which the trays arereturned towards the loading station with the usual lower translatingmeans. All the other trays not included in the short cycle must remainstationary.

The invention is designed to overcome these and other drawbacks of thevertical kilns according to the known art, by the following idea for asolution.

The trays are provided at their corners, for example at the ends of thelong sides, with vertical spacers, projecting upwards for example, whichare identical and enable stacks to be formed in which the trays rest onone another and are spaced apart with a desired interval. The spacersare preferably such that their upper ends interact with suitable seatsformed on the bases of the trays lying above, in such a way that thestacked trays are perfectly centered with respect to each other. In thiscase, the rising and descending movement of the trays in the consecutivestacks of the kiln is achieved by means of elevating and loweringdevices which act on the bottom tray of each stack, grippers beingprovided in the stacks with ascending movement to retain the bottom trayof these stacks in position, to enable the ascending means to return tothe low position for the repetition of a new cycle. In the stacks with adescending movement, similar grippers are provided to keep the tray nextto the bottom held in the high position, while the elevating andlowering device supports the bottom trays of the stacks on the lowertranslating device such as a conveyor. The trays, held by the gripper,are at such a height that they do not interfere with the lower traytranslated by the lower translating device. For the upper translation ofthe trays from the top of one stack to that of the adjacent stack, it ispossible to provide chain conveyors parallel to the short sides of thetrays, outside the stacks of the trays, and it is possible to associatethese conveyors with means which, at the appropriate time, slightlyraise the trays to be translated and which then translate the trays anddeposit them on the trays of the receiving stack.

Clearly, the new solution makes it possible

to eliminate the conventional elevating and lowering chain conveyors T1and T2 (FIGS. 1 and 2) and to overcome all the drawbacks arising fromthe use of such conveyors;

to place the conveyors for translating the trays from one stack to theadjacent stack outside the plan dimensions of the stack of trays andthus to eliminate the drawbacks arising from the use of the conventionaltranslating devices of the type shown by T3 in FIGS. 1 and 2;

if the kiln is to be used for operation with a short cycle, it is simpleto place a supplementary translating device, similar to the upper means,at the desired height of the stacks of trays, to move a limited numberof trays along a short path closed in a loop between the loading andunloading stations, and it is simple to use the supplementary elevatingdevice to raise the stacks of trays not included in the short path, torelease them from the action of the lower elevating and lowering device.The auxiliary translating device for the short cycle is also locatedoutside the plan dimensions of the trays and cannot deposit dirt on thedried articles.

BRIEF DESCRIPTION OF DRAWINGS

Further characteristics of the invention, and the advantages derivedtherefrom, will be made clearer by the following description of apreferred embodiment of the invention, illustrated purely by way ofexample and without restrictive intent in the figures of the attachedsheets of drawing, in which

FIGS. 1 and 2 are schematic views, from the side and the frontrespectively, of a known two-stack kiln, of the type described in theintroduction to the present description;

FIGS. 3, 4 and 5 are schematic views, in plan from above and in lateraland frontal elevation respectively, of a two-stack kiln according to theinvention;

FIG. 6 shows a detail of a spacer of a tray, shown by transverselycutting a side member of the tray at the point where the said spacer isfitted;

FIG. 6a shows a variant embodiment of the tray spacer, shown as in FIG.6;

FIG. 7 shows on an enlarged scale and from the side, as in FIG. 4, astack of trays of the kiln, with the corresponding means of moving thetrays vertically, shown in the high position;

FIG. 8 is a front elevation of the stack of trays of FIG. 7, with meansof moving the trays vertically, in the high position;

FIG. 9 shows, in a front elevation and in the low and retracted restposition, one of the means of moving the trays vertically;

FIG. 10 shows, in a plan view from above and with parts in section, oneof the forks which hold the trays in the raised position in the stacks;

FIG. 11 shows, in a front elevation and in the rest stage, one of theauxiliary forks which, on command, raise the trays not included in theshort cycle;

FIGS. 12 and 13 are lateral and front views respectively, with parts insection, of the lower translating conveyor which transfers the traysfrom the unloading station to the loading station;

FIG. 14 shows from the front, in partial section and in the activestage, one of the upper translating tray conveyors;

FIG. 15 shows in a perspective view one of the hook-shaped wheeledoscillating tray-gripping levers of the conveyor of FIG. 14;

FIG. 16 shows from the side the means which raise and lower thehook-shaped tray-gripping levers of the conveyor of FIG. 14;

FIG. 17 is a schematic plan view from above of one of the supplementarytranslating conveyors for moving the trays in the short cycle path;

FIGS. 18 and 19 are front views of the translating conveyor of FIG. 17,in the rest position and in the active position respectively;

FIGS. 20 and 21 show schematically and in lateral elevation a two-stackkiln shown in successive stages of a normal operating cycle;

FIGS. 22, 23, 24 and 25 show schematically and in lateral elevation akiln with two stacks of trays, shown in hypothetical successive stagesof operation in a short cycle;

FIG. 26 is a schematic lateral view of a possible embodiment of themeans of moving the trays in a four-stack kiln.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 3 to 8, it can be seen that, in the kiln inquestion, use is preferably made of trays V of the type with a conveyorbelt base which can be operated from a power take-off located at the endof each tray, so that it is not necessary to have conveyors with poweredrollers under the trays at the loading and unloading stations; theseconveyors would be required if the trays were of the type with a latticebase. However, it is to be understood that the kiln according to theinvention is also considered to be protected even if adapted to the useof trays with lattice bases. The details of FIGS. 7 and 8 show that thetray V comprises two strong side-members 1, preferably made from aC-section or equivalent, interconnected by a flat stiffening structurewhich, at least at the ends, carries rollers around which runs theconveyor belt 2 which forms the base of the tray on which the articlesto be dried are placed. The side-members 1 have a height greater thanthat of the conveyor base 2 and rise above the latter to contain thefull height of the articles to be dried. The number 3 shows the powertake-offs located on the outer sides of the side-members 1 and buttingagainst at least one of the end rollers of the conveyor 2, to whichrotation means of a known type are coupled when the trays reach thearticle loading and unloading stations, so that the upper branch of thetray conveyor advances at the same speed and in the same direction asthe articles supplied by a conveyor T which is external to the kiln, andis aligned and coplanar with the tray conveyor 2 (FIG. 8).

According to the invention, as shown in FIGS. 6, 7 and 8, a shank 104 ofa spacer 4 which, for example, projects from the top of the side-memberand is, for example, provided with a conical or truncated conical head204 with its diameter decreasing towards the top (see below) is weldedin a suitable vertical seat at each end of the side-member 1 of eachtray. The shank of each spacer 4 is suitably withdrawn from the base ofthe seat which houses it, so that a lower part S of this seat remainsfree and can be shaped in the form of a funnel to receive the top of thehead of a spacer 4 when a plurality of trays of the type in question arestacked on top of each other as in FIGS. 7 and 8. The seats S whichhouse the spacers 4, and the spacers themselves, are also preferablydesigned in such a way that, when the trays are stacked on top of eachother, the spacers of the various trays are aligned axially with eachother and bear on each other, in other words that the top of the head ofone spacer touches the lower end of the shank of the spacer locatedabove. The height of the spacers 4 is such that, when a plurality oftrays are stacked on top of each other, the necessary space is leftbetween the trays to contain, with clearance, the articles to be dried,and to allow the drying air to circulate freely.

Because of the presence of the spacers 4, which create the intervalbetween the various trays, it is possible to dispense with theconventional chain conveyors T1 and T2 of the known art (FIGS. 1, 2),since the elevation and lowering of the trays in the adjacent stacks C1and C2 of a kiln as illustrated for example in FIGS. 3 and 5 can now becarried out by using means which elevate and lower only the bottom traysof the said stacks C1 and C2 by one step, in a cyclical way. Theelevating and lowering system or device such as the elevating andlowering means BM usable for this purpose preferably act on the ends ofthe side-members 1 of the trays and can be of any type suitable for thepurpose. Preferably, the elevating and lowering means are operated byconnecting rod and crank systems which are moved by a common shaft whichcan be driven by a minimum force, since the systems are approximately180° out of alignment and essentially balance each other, since theweight of the trays in the stack C2, which have to descend by one stepin each cycle, discharges positive energy on to the shaft which operatesthe connecting rod and crank systems for elevating the trays in thestack C1.

FIGS. 7 and 8 show that the frame of the kiln has, at the positions ofthe ends of the side-members of the trays placed in the stacks C1, C2,uprights 5 on which are fixed vertical guides 6, of C-section forexample, in which there run the rollers 7 of carriages 8 to which arepivoted at 9 connecting rods 10 which are orientated downwards and arepivoted at 11 on cranks 12 keyed with identical orientation on ahorizontal shaft 13 supported rotatably by supports 14 fixed to theframe of the kiln. The number 110 indicates a cross-pieceinterconnecting each pair of connecting rods 10 of the means inquestion. The shaft 13 which carries the cranks for the stack C1 isconnected by a positive transmission 15 to a parallel shaft 16 connectedto a driving motor unit 17, of the type with electronic speed and phasecontrol for example. The motion for the operation of the shaft with thecranks for the stack C2, which are out of alignment by approximately180° with the cranks 12, is taken from the shaft 16 through a positivetransmission, not shown in FIG. 7, identical to that indicated by 15.

A lever 19, of essentially triangular shape for example, has one of itsvertices pivoted at 18 on each carriage 8, parallel to the shafts 13 and16, and has a second vertex pivoted at 20 on the rod of an actuator 21,for example a jack which in turn is pivoted at 22 on an extension of thetrolley 8. Depending on whether the rod of the jack 21 is extended orretracted, the third upper vertex 119 of the lever 19 is, respectively,located under the plan dimensions of a side-member 1 of a tray, as shownin FIG. 8, to raise or lower the tray through one step in the stack C1or C2 of the kiln of FIGS. 3, 5, or withdrawn outside the stacks oftrays, as shown in FIG. 9, so that it can return to the low position ofthe stack C1 or the high position of the stack 2, to repeat a newoperating cycle without interfering with the tray driven by the lowertranslating device (see below).

The system of elevating the trays in the stack C1 (FIGS. 3-5) is suchthat the raised bottom tray in this stack is at a height where it doesnot interfere with the future empty tray which will be translated fromthe base of C2 to C1 (see below). Since the operating cycle of the kilnrequires that the elevating system BM of C1 reverse its movement afterthe elevation travel, to permit the neutralization of the correspondinglevers 19 and to return to the low position of the start of the cycle,means are provided in the stack C1 to hold in the high position the basetray which is cyclically raised and placed in the station K1 for loadingthe articles to be dried. These means are shown in FIGS. 7, 8 and 10,and consist of horizontal forks 25, mounted for example on the uprights5 of the kiln frame, which are normally in a position ofnon-interference with the trays and which, on command, are extended andinserted, for example, into the upper projecting parts of the fourspacers 4 of the raised tray, under the heads of the spacers, so thatwhen the levers 19 of the elevating means of the stack C1 are lowered,all the trays of the stack C1 remain in the high position where they donot interfere with the subsequent empty tray which will then betranslated by the lower translating means from the stack C2 to the stackC1.

FIGS. 7, 8 and 10 show, for example, that each fork 25 slides in guideseats 26 formed in a pair of plates 27, parallel to each other,positioned sideways, welded to the upright 5 and interconnected ifnecessary by a stiffening cross-piece 27′. On the plate 27 opposite thatfrom which the active end of the fork 25 is designed to project, thereis fixed horizontally the body of a jack 28, whose rod is parallel tothe said fork, passes through an aperture in the said plate 27 and isfixed to a cross-piece 29 integral with the fork, which can be movedlongitudinally by the rod of the jack 28.

In the subsequent stage of raising of a tray in the loading station K1,it is specified that when the spacers 4 of this tray come into contactwith the base of the tray held by the forks 25 of C1, these forks areretracted to permit the raising of the new tray and of the wholeoverlying stack of trays, and these forks are only reactivated at theend of the elevation travel, to hold the new bottom tray of the stack C1at the correct height. In the kiln with two stacks of trays shown forexample in FIGS. 3-5, forks 25, identical to those described for thestack C1, are provided to hold the bottom tray of the stack C2 in araised position in which it does not interfere with the underlying traywhich the lowering device has previously lowered from the lower part ofthis stack and have transferred on the carriages 23 of a lowertranslation device such as a pair of horizontal chain conveyors 24, 24′which are parallel to each other, orthogonal to the side-members of thetrays and placed to form a link between the stacks C1, C2 (see below).

When a tray reaches the carriages of the translating conveyors 24, 24′,the lowering device of the stack C2 undergo a small additional downwardtravel to allow the levers 19 of the system to be detached from theside-members of the lowered tray and to be retracted into the restposition of FIG. 9. When the translation of the tray by the conveyors24, 24′ has been completed, or in step with this translation, thelowering device of C2 returns to the high position, with the levers 19which at the appropriate time are extended and positioned under the baseof the tray held by the forks 25 of C2. When the levers 19 have touchedthe bottom tray of C2, the forks 25 of this stack are retracted and allthe trays of the stack C2 are lowered by the lowering device with thelevers 19. The lowering of the trays in C2 is stopped temporarily ordecelerates when the spacers of the next-to-bottom tray of C2 reach theheight of the forks 25, which are activated at the correct time to holdthis tray together with the trays above it, after which the loweringdevice is restarted or accelerate and return to the original speed, todeposit the tray associated with these on the carriages 23 of the lowertranslating conveyors 24, 24′, in such a way that this tray is suitablyspaced apart from the new bottom tray of C2 and can be translated by theconveyors 24, 24′. The tray held by the forks 25 in the stack C2interacts with the means of the unloading station K2 which remove thedried products from it.

The following flow chart indicates the sequence of the operating stepsof the elevating and lowering system which operate in the stacks C1 andC2.

C1 C2 Levers 19 active, start of upward movement Levers 19 are active,forks 25 are disabled and raising of tray from the conveyor 24, 24′ andlowering of all trays commences Contact of raised tray with bottom trayof Lowering of all trays of C2 C1, forks 25 are disabled and all traysof stack C1 are raised Raised bottom tray aligned with loadingNext-to-bottom tray aligned with unloading station K1, forks 25 of C2come into station K2, forks 25 act on it as the lowering operation withhalt or deceleration of device stops or decelerates elevator andneutralization of levers 19 The inactive elevator passes through an Traycarried by the lowering device additional idle upward travel descends,comes to rest on the conveyor 24-24′ and is released by theneutralization of levers 19 Inactive elevator descends and stops orLowering device is raised and stops or decelerates slightly before thelower end stop decelerates slightly before the upper end stop Elevatorcompletes its descent and levers Levers 19 are activated and thelowering 19 are activated under the tray device completes its upwardtravel to contact the tray.

If necessary, the vertices 119 of the levers 19 of the elevating andlowering system which operate in the stacks of trays of the kiln can beprovided with small projections which are used for centering in thelower seats S of the trays under the spacers 4 of the trays.

FIGS. 12 and 13 show that the lower translating conveyors 24, 24′comprise corresponding rectilinear base structures 30, 30′, the ends ofwhich carry sprockets with horizontal axes 31, 31′, a pair of which isinterconnected by a shaft 32 which in turn is connected to a commonsource of intermittent rotary motion (not illustrated). Around thesprockets 31, 31′ there run chains 33, 33′ to which are fixed U-shapedcarriages 23, 23′, whose wheels 34, 34′ run in guides 35, 35′ associatedwith the structures 30, 30′. In passing along the upper branch of theconveyors 24, 24′, the carriages 23, 23′ project suitably from thecorresponding guides 35, 35′, so that the tray V which is cyclicallycarried on these carriages does not interfere with the guides. Thecarriages 23, 23′ can advantageously be provided on their opposite endswith projections 36, 36′ which act as centring devices and which preventundesired movements of the trays during the translation.

FIGS. 3 and 5 show how, in the kiln in question, owing the absence ofconventional chain conveyors for the raising and lowering of the trays,it is possible to place at the tops of the stacks C1 and C2, parallel tothe short sides of the trays and outside the stacks, conveyors of anytype 37, 37′ which act in step with each other to hold the top tray ofthe stack C1, raise it suitably to space it apart from the underlyingtray, and translate it on to the stack C2, depositing it on the top trayof this stack. These conveyors, being placed at the sides of the stacksof trays, cannot deposit dirt on the trays, as can occur in the knownart.

According to the invention, the upper translating conveyors 37, 37′ aredesigned to hold the tray to be translated by its spacers 4, as will nowbe described with reference to FIGS. 5, 14, 15 and 16. The conveyors inquestion comprise corresponding support structures fixed to, andprojecting from, the frame of the kiln, the ends of these structurescarrying rotatable sprockets 38, 38′ (FIG. 5) with horizontal axes,around which run chains 39, 39′ (FIG. 3) whose rectilinear branches arecontrolled by guides 40 (FIG. 14) fixed to the said support structure.Carriages 41 (FIGS. 14, 15), each provided with a pair of wheels 42which run on a rectilinear fixed guide 43, at least when passing alongthe lower branch of the conveyors in question, are fixed to the chainswith the same spacing between them as that found between a pair ofspacers 4 at one end of a tray V. The carriages 41 are of forked shape,so that the intermediate part of a corresponding flat lever 45 can bepivoted to them at 44, the portion of the lever facing the stack oftrays being shaped in the form of a horizontal hook 145, with itsaperture orientated in the direction of translation of the trays. At itsend opposite the hook-shaped end, the lever 45 carries a roller 46 witha horizontal axis, which as it passes along the lower and upper branchesof the conveyors runs in grooved guides 47, 47′, the latter of which isfixed. The lower guide 47 can be moved vertically on command to causethe oscillation of the levers 45 required for the raising and loweringof the tray. FIGS. 14 and 16 show how the guide 47 is pivoted at 48 onconnecting rods 49 which in turn are pivoted at 50 to one of thevertices of a corresponding number of triangular plates 51, pivoted at52 on the fixed support structure G of the conveyor. The third vertex ofeach plate 51 is pivoted at 53 to the rod of a respective jack 54, thebody of which in turn is pivoted at 55 to the said fixed structure G.The number 78 indicates a connecting rod for synchronizing theoscillatory movement of the plates 51. Clearly, after the retraction ofthe rods of the jacks 54, the double guide 47 is raised and the activeends of the hook-shaped levers 45 are lowered, whereas when the rods ofthe said jacks 54 are extended, the double guide 47 is lowered, raisingthe said hook-shaped levers 45. The conveyors 37, 37′ are synchronizedby an interconnecting shaft 56, part of which appears in FIG. 14 and inFIG. 5, which show how the conveyors 37, 37′ act on the trays V with thelevers 45 which travel along the lower branches of these conveyors.These figures also show how the distance between the two frames of eachconveyor 37, 37′ is such that the levers 45 passing along the upperbranch do not interfere with the spacers 4 of the trays translated fromthe lower branch by the conveyors in question.

The conveyors 37, 37′ operate in the following way. FIGS. 3, 5 and 20,21 show the stages of operation of a two-stack kiln in the normal cycle.At the start of the cycle, the conveyors 37, 37′ are in the restposition, with corresponding pairs of hook-shaped levers 45 above thestacks C1 and C2, in the low position and suitably retracted in thedirection of operation with respect to the vertical alignments with thespacers 4 of the trays in each stack. FIG. 2 shows the instant at whichthe elevating and lowering system of the connecting rod and crank typeBM have raised and lowered the trays in the stacks C1 and C2respectively, and when the forks 25 have acted to keep the new bottomtrays of the stacks C1, C2 raised, to enable the elevating and loweringsystem to reverse its motion.

After this step, the trays of the stack C2 are aligned horizontally withthe adjacent trays of the stack C1, and there is a tray missing from thetop part of the stack C2 so that the step of transferring a tray fromthe top part of C1 to that of C2 can take place. FIG. 21 illustratesthis step. The conveyors 37, 37′ are started and a pair of theirhook-shaped levers 45, in the low position, is inserted, for example,under the heads of the spacers 4 of the top tray of C1, after whichthese levers swing upwards and raise the tray which can thus betransferred from C1 to C2 without interfering with the underlying trays.When the translated tray has reached C2, the conveyors 37, 37′ stop,their levers 45 of the lower branch are lowered to deposit thetranslated tray on the underlying tray of C2, and then the conveyors 37,37′ reverse their motion to retract their levers 45 from the spacers ofthe trays located at C1, C2 and to position themselves at rest, as shownin FIGS. 4 and 20, to enable the operating cycle to be repeated.

The kiln according to the invention can be set up to operate with ashort cycle as described in the patent cited in the introduction to thisdescription background section above, by placing auxiliary conveyors atthe sides of the stacks C1 and C2, at the desired height, to translatethe trays from C1 to C2, and by using means in addition to the forks 25to raise the upper trays of C1 and C2 which are not included in theshort cycle.

The auxiliary translation conveyors could be of the same type as theupper conveyors 37, 37′, but with the possibility of carrying outhorizontal movements towards and away from the stacks of the kiln, sothat the levers 45 of these conveyors do not normally interfere with therising and descending movements of the trays. Alternatively, theauxiliary translation conveyors can be of a dedicated type, as describedbelow with reference to FIGS. 17-19.

Each auxiliary translation conveyor 57 comprises rectilinear parallelguides 58, 58′ on the ends of which are fixed plates 59, 59′ which carrysprockets 60, 60′ which are rotatable about vertical axes and aroundwhich a chain 61 is run and tensioned, the opposite branches of thischain running in the said guides 58, 58′. Teeth 62, fixed to the chain61 in the correct number and at suitable intervals, are normally locatedoutside the plan dimensions of the stacks of trays of the kiln. Eachtooth 62 can be provided at its top with a roller 63 with a verticalaxis, which, as it passes along the rectilinear branches of the conveyorin question, interacts with dedicated parts of the guides 58, 58′. Thechain of one conveyor 57 is clearly synchronized with that of theauxiliary opposite conveyor 57′. At a short distance from the guides 58facing the trays of the kiln, there is a parallel beam 64, fixed to theend plates 59, 59′, and supporting rotatably by support means 65 aparallel shaft 66 on which are keyed L-shaped levers 67 in a sufficientquantity to support three portions of rectilinear rails 68, 68′ and 68″which are aligned with each other and parallel to the said shaft 66. Theend rails 68, 68″ are of such a length that they can be inserted underthe short sides of the trays, without interfering with the lower seats Sof the trays, in which, or in the vicinity of which, the spacers 4 of anunderlying tray may be located (see below).

Some of the levers 67 are pivoted at their elbows, at 69, on the rods ofjacks 70 pivoted by their bodies 71 on cross-pieces 72 shaped in theform of an inverted U and fixed between the beam 64 and the guide 58′.By the movement of the jacks 70, the rails 68, 68′, 68″ can be retractedinto the rest position shown in FIG. 18, under the plan dimensions ofthe conveyor 57, 57′, or can be raised and extended as shown in FIG. 19,for insertion under a tray, the tray being slightly raised if necessary.

The other means required for the operation of the kiln in a short cycleare shown in FIG. 11, and comprise forks 25′, identical to the forks 25of FIG. 10 except in that the guide plates 27 are fixed on a slidingblock 73 slidable on a vertical guide 74 fixed to the upright 5, onwhich is also fixed the body of a jack 75 which is fixed by its rod tothe sliding block 73. Thus the auxiliary fork 25′ can undergo a verticalraising and lowering movement of the correct extent, in addition to thenormal horizontal movement towards and away from the trays (see below).

With reference to FIGS. 22-25, a description will now be given of theway in which a kiln of the type in question can be set up to operatewith a short cycle. In FIG. 22, for example, it is assumed that theoperation of the kiln with a short cycle takes place with thetranslation from C1 to C2 of the tray which is above that which iscyclically held by the forks 25 of C1, and therefore the auxiliaryconveyors 57, 57′ have been located at this height, only one of theseconveyors being visible in the rest position as shown in FIG. 18.

Auxiliary forks 25′ are provided in the stack C2 to act, on command, onthe tray above that located at the height of the conveyors 57, 57′. FIG.22 shows the point of the cycle at which an empty tray from the stack C2has been transferred by the conveyors 24, 24′ into the stack C1 where,at the station K1, there is for example an empty tray which is loadedwith products to be treated in the short drying cycle. In the stack C2,a tray is located at the station K2, for example, for unloading theproducts dried by the normal cycle, and the tray located above K2 alsocontains, for example, products treated by the normal cycle. The forks25 are active in both stacks C1 and C2. The upper conveyors 37, 37′ havetheir hook-shaped levers 45 in the retracted rest position and arestationary. In the stage shown in FIG. 23, the auxiliary forks 25′ ofthe stack C2 have raised the trays located above the tray which is atthe height of the translation conveyors 57, 57′, while the loweringmeans BM hold the tray emptied at K2 and the forks 25 are disabled toallow the descent of the two trays. FIG. 24 shows how the tray which waspreviously at K2 has been transferred to the carriages 23 of the lowerconveyors 24, 24′ and how the tray located above has been held by theforks 25 at the unloading station K2. Meanwhile, in the stack C1, theelevating means BM have been started to insert a new empty tray into theloading station K1, while the previously filled tray has been raised tothe height of the conveyors 57, 57′.

In the following stage shown in FIG. 25, the auxiliary forks 25′ in thestack C1 come into action, to raise all the trays above the tray filledwith the product for the short cycle, which is then transferred, by theauxiliary conveyors 57, 57′ which are started at the correct time, fromC1 to C2, while a new empty tray is transferred from C2 to C1 by thelower conveyors 24, 24′ The short cycle continues with only four traysincluded in the cycle of raising and lowering and upper and lowertranslation, while all the other trays remain stationary and can containproducts from a preceding normal operating cycle.

In the cycle described with reference to FIGS. 22 to 25, it is clearthat, after the intervention of the auxiliary forks 25′ in the stack C2,the elevating and lowering means BM of the two stacks are unbalanced, inthat the weight of six trays bears on the elevating means of the columnC1, while the weight of only two trays bears on the lowering devices ofthe column C2 (see FIGS. 23, 24). This unbalancing causes an excessiveload on the geared motor which drives the elevating and lowering means,and which for this reason has to be designed with excess capacity. Toavoid this problem, the auxiliary forks 25′ of the stack C1 can be madeto act simultaneously with the action of the auxiliary forks 25′ of thecolumn C2, to raise the trays, starting from that located at the heightof the auxiliary conveyors 57, 57′, in such a way that the kilnimmediately enters the condition shown in FIG. 25, with equal numbers oftrays resting on the elevating and lowering means of the columns C1 andC2. It is to be understood that other means can be provided for thispurpose.

It is to be understood that conveyors of the same type as 57, 57′ can beused in place of the upper translation conveyors 37, 37′.

It is also to be understood that kilns with more than two stacks oftrays also lie within the scope of the invention.

FIG. 26 shows, for example, a kiln of the normal cycle type, with fourstacks of trays C1, C2, C3 and C4, provided with correspondingconnecting rod and crank elevating and lowering means as describedabove, and with corresponding forks 25. The kiln is provided with theusual lower conveyors 24, 24′ for translating the bottom trays from C4to C1, and with the usual upper conveyors 37, 37′ for simultaneouslytransferring a tray from C1 to C2 and from C3 to C4. To transfer thetrays from the lower part of C2 to the lower part of C3, it is possibleto use simple means which comprise horizontal fixed guides 76 forsupporting the ends of the trays to be transferred, and which havelateral conveyors with pushing teeth 77, 77′ similar to those used inthe conveyors 57, 57′ to translate the tray from C2 to C3. The conveyors77, 77′ and the guides 76, if located at a suitable level, can bereplaced with conveyors 57, 57′ for the short cycle, if these arearranged in a number of portions or sections located one after another,and if they are set up to have only the central section operating totransfer the trays from C2 to C3 in the normal cycle and to operate withall the sections combined in the short cycle, to transfer a traydirectly from C1 to C4.

Another variant may relate to the fact that the spacers 4 have adifferent shape from that considered with reference to FIG. 6, to carryout the sole function of spacing, and if necessary centring, the stackedtrays. For example, FIG. 6a shows the use of spacers 4 of a completelycylindrical shape without heads. In this case, the gripping of the traysby the grippers 25 and 25′ which operate in the different stacks of thekiln can take place by the insertion of the grippers into the lateralcavities of the side-members and of the frames 1 of the trays, with thegrippers bearing on the upper edges of the said side-members, asindicated by the broken line, or with the said grippers inserted intothe spaces between the stacked trays and bearing on the bases of thesetrays, as indicated by the chained line. In the same way, the uppertrays of the stacks can be held by the levers 45 of the uppertranslation conveyors 37, 37′, provided that these are designed to bemoved away from and towards each other at the correct time, so that thesaid levers do not interfere with the trays when they are at rest.Alternatively, the upper conveyors 37, 37′ can be replaced withtranslation conveyors of the type indicated by 57, 57′.

A further variant may relate to the fact that the spacers 4 project fromthe bases of the trays instead of from their tops.

It is to be understood that the programming, control and safety means ofthe kiln have been omitted from the description, since they are readilyunderstandable and can easily be constructed by those skilled in theart.

What is claimed is:
 1. A vertical kiln comprising a drying chamberhaving two or more vertical and adjacent stacks of horizontal trayswhich are made to rise by steps in one stack and then to descend bysteps in the next stack via an elevating and lowering system, and whichare moved along horizontal translatory paths by a lower translationdevice for the transfer from the top of one stack to that of theadjacent stack and for the transfer from the end of the last stack tothe start of the first stack, where stations for unloading and loadingarticles from and into the trays operate in operable positions, theelevating and lower system comprising, outside the stacks of trays, onthe short sides of the trays, in the lower parts of the stacks, and in aquantity equal to one for each corner of the bottom tray to be raisedand lowered, vertical guides integral with corresponding uprights of akiln frame, on which slide corresponding carriages, each of whichcarries a lever pivoted parallel to the short sides of the trays, thelever being controlled by a jack which can bring an upper extension ofthe lever into an active position of projection under the corner area ofthe tray to be raised or lowered, or into a retracted position ofnon-interference with the trays, the carriages of the adjacent stacks oftrays of the kiln operable in opposite elevating or lowering movements,wherein the trays arranged with vertical spacers so that the trays canbe stacked on top of each other with sufficient spacing between them,and can be raised and lowered in the adjacent stacks by the elevatingand lowering system which operates on the bottom trays of the stacks, topick up and deposit the trays on the lower translation device at anappropriate time, a lowering device of the elevating and lowering systemtransferring an empty tray from a last stack to a first stack of thekiln, a bottom tray of the last stack being held at a given height,above the lower translation device, by grippers which are activated anddisabled in step with the elevating and lowering system.
 2. The verticalkiln according to claim 1, wherein the spacers are at least four innumber and each is mounted vertically in a corner area of each tray andprojects from the top of the tray.
 3. The vertical kiln according toclaim 1, wherein the spacers are located on the outer edges of the longsides of the trays providing a large portion of the short sides of thetrays to remain free for gripping, by the translation device when thetrays are stacked.
 4. The vertical kiln according to claim 1, whereineach spacer projects from an upper part of the tray with a portion of arespective shank and when a plurality of trays are stacked on top ofeach other, an upper end of each of the spacers engages with an openfunnel-shaped seat on a base of each tray, provided at a lower end of ahole formed in a side of the tray into which the shank of each spacer isinserted and welded, thereby providing mutual centering of the stackedtrays.
 5. The vertical kiln according to claim 4, wherein a lower end ofthe shank of each spacer reaches into the open funnel-shaped seatcontaining an upper end of a respective spacer when a plurality of traysare stacked on top of each other, whereby the spacers of the stackedtrays touch each other.
 6. The vertical kiln according to claim 1,wherein the trays have frames with side-members having an outwardly openprofile, the spacers being located at the ends of the side-members beinglocated inward from outer sides of the spacers or partially projectingfrom the outer sides of the spacers.
 7. The vertical kiln according toclaim 4, wherein the spacers are provided with heads tapered towards atop of the spacers.
 8. The vertical kiln according to claim 4, whereinthe spacers are in the form of rods, and have upper ends flared orrounded.
 9. The vertical kiln according to claim 1, wherein the trayshave bases in the form of conveyor belts or with latticed bases.
 10. Thevertical kiln according to claim 1, wherein the elevating and loweringsystem is driven with a travel longer than the interval between thestacked trays, to allow the levers of the elevating and lowering systemto carry out without interference, oscillatory activating and disablingmovement and to ensure that a tray held at an appropriate height by thegrippers does not interfere with a tray subjected to the action of thelower translation device.
 11. The vertical kiln according to claim 1,wherein the carriages of the levers are connected by connecting rodswhich in turn are pivoted on cranks keyed on the ends of shafts parallelto the short sides of the trays, and which, via positive transmissionsof motion, receive an intermittent motion from a parallel main shaftdriven by a motor unit with electronic or electromechanical speed andphase control.
 12. The vertical kiln according to claim 7, wherein thegrippers which hold the lowest trays of the stacks at an appropriateheight, above the lower translation device which cyclically transfers atray from a last stack to a first stack of trays of the kiln, areprovided with a movement towards and away from the trays, and are suchthat the grippers act on portions of the spacers located underrespective heads of the spacers, whereby the heads bear on the grippers.13. The vertical kiln according to claim 8, wherein the grippers whichhold the lowest trays of the adjacent stacks an appropriate height andwhich are provided with a movement towards and away from the trays,wherein the grippers act in an open cavity of a respective tray towardsthe exterior of side-members of a frame of the respective tray, andwherein the grippers bear on upper edge of the side-members.
 14. Thevertical kiln according to claim 8, wherein grippers which hold thelowest trays of the stacks at an appropriate height and which areprovided with a movement towards and away from the trays, bear onrespective bases of side-members of frames of the trays.
 15. Thevertical kiln according to claim 1, wherein the gripper which holds thelowest trays of the first and last stacks at the appropriate heightcomprise forks orthogonal to short sides of the trays, supported by ahorizontal guide which is fixed to uprights of a frame of the kiln andon which the forks can be moved longitudinally by jacks which can bringactive edges of the forks from a rest position, in which the edges areretracted from the trays, to a position of gripping the tray to be heldat the appropriate height, in which the active edges of the forks arefitted around the shanks of the spacers of the tray or under the tray.16. The vertical kiln according to claim 1 wherein the lower translationdevice comprises a pair of parallel and horizontal conveyors havingpositive transmission, the pair of parallel and horizontal conveyorshaving carriages fixed thereto which, as the carriages pass along anupper branch of the conveyors, project from corresponding fixed guidesto receive intermediate parts of side-members of the frame of the kiln,the carriages being provided with opposite end projections which act tocontain the tray, to prevent the tray from moving in undesired waysduring a translation stage.
 17. The vertical kiln according to claim 1,further comprising an upper translation device which cyclicallytransfers a tray from the top of one stack of trays, which has anascending movement, to the top of the adjacent stack of trays, which hasa descending movement, the upper translation device comprisinghorizontal chain conveyors located at the sides of the tops of thestacks and parallel to the short sides of the trays, the chains of eachconveyor running around end sprockets with horizontal axes, rectilinearbranches of the chains being controlled by rectilinear guides whichleave free one side of each chain, to which are fixed carriages spacedapart with the same distance between centers as that found between twospacers located on a short side of a tray, the carriages being providedwith rollers which, as the carriages pass along a lower branch of theconveyor, run on a rectilinear fixed guide, and the carriages havinglevers pivoted parallel to the chains flat ends of these levers, shapedinto horizontal hooks projecting towards the stacks of trays, above theplan dimensions of the stacks and with the opening of the hooksorientated in the direction of translation of the trays, while theopposite end of each of the levers carries a roller which as it passesalong the rectilinear branches of the conveyor, interacts withrectilinear guides the lower of which is grooved, double-acting, and isconnected to the elevating and lowering system, for lowering andelevating, the hook-shaped ends of the levers, respectively, thehook-shaped levers gripping the upper tray of the stack with theascending movement as the hook-shaped levers pass along the lower branchof the conveyor, by upper projecting parts of corresponding spacers,under heads of the respective spacer, after which the levers rotate toraise the gripped upper tray, to space the gripped tray apart from theunderlying tray and to enable the gripped tray to be translated, whileon completion of the translation, the levers rotate in the oppositedirection, to lower the translated tray and deposit the tray on theunderlying tray, after which the conveyor reverses movement to retractthe hook-shaped levers, to bring the hook-shaped levers to a position inwhich the hook-shaped levers do not interfere with the spacers of theupper trays of the stacks.
 18. The vertical kiln according to claim 1,wherein, when the kiln contains more than two adjacent stacks of trays,the lower translation device is adapted to cyclically transfer a lowertray of a stack of trays with a descending movement to the bottom of theadjacent stack of trays with ascending movement, the lower translationdevice having fixed lateral guides on which the tray to be translated issupported, and being provided with chain conveyors running aroundsprockets with vertical axes, located outside the stacks, parallel tothe guides and to the short sides of the trays, and provided withpushing teeth which at the correct time push the tray so that it slideslongitudinally on the guides.
 19. The vertical kiln according to claim1, wherein the translation device provides a path for at least a limitednumber of trays to carry out an annular movement along a short path in ashort cycle as compared with a normal path in a normal cycle whereby thelimited number of trays are raised to pass into a loading station, andthen raised by one or more steps and then translated towards final stackwhere the trays descend to pass into an unloading station and thendescend and are translated back into a first stack, under the loadingstation, for the repetition of the short cycle.
 20. The vertical kilnaccording to claim 19, further comprising an auxiliary means for raisingand holding trays not included in the short cycle the auxiliary meanshaving auxiliary conveyors for translating the trays not included in theshort cycle from the first stack with an ascending movement to the laststack with a descending movement.
 21. The vertical kiln according toclaim 20, wherein the auxiliary means comprises forks fixed to theuprights of the frame of the kiln with the interposition of a verticalguide and sliding block unit connected to a raising and loweringactuator.
 22. The vertical kiln according to claim 20, wherein theauxiliary conveyor provide for movement towards and away from the stacksof trays, wherein in the normal operating cycle of the kiln, thehook-shaped levers of the auxiliary conveyors do not interfere withnormal movement of the trays.
 23. The vertical kiln according to claim22, wherein the auxiliary conveyors can be used to translate the traysbetween the tops of the stacks when oscillating levers of the auxiliaryconveyors act in cavities of frames of the trays or on bases of thetrays.
 24. The vertical kiln according to claim 20, wherein theauxiliary conveyors comprise rectilinear conveyors parallel to upperconveyors, the rectilinear conveyors having chains running aroundsprockets with vertical axes and with teeth, the rectilinear conveyorscan carry out translation of the trays by pushing the trays, rails beingprovided under active branches of the upper conveyor and rectilinearconveyor and parallel to the upper conveyor and rectilinear conveyor,the rails being fixed to oscillating levers and connected to actuatorswhich hold the rails in a retracted position in which the rails do notinterfere with the trays, but which, can translate the rails and insertthe rails under the tray or trays to be translated so that the railsbear on these trays and raise the trays in the appropriate way.
 25. Thevertical kiln according to claim 17, further comprising rectilinearconveyors with movable rails which can be used in place of thehorizontal chain conveyors.
 26. The vertical kiln according to claim 24,wherein the auxiliary means can be made in sections with independentmovements such that the auxiliary means can provide the translation ofthe trays between lower parts of intermediate stacks of a kiln havingmore than two adjacent stacks of trays, when the kiln is operating witha normal cycle.
 27. A vertical kiln comprising a drying chamber havingtwo or more vertical and adjacent stacks of horizontal trays which aremade to rise by steps in one stack and then to descend by steps in thenext stack via an elevating and lowering system, and which are movedalong horizontal translatory paths by a lower translation device for thetransfer from the top of one stack to that of the adjacent stack and forthe transfer from the end of the last stack to the start of the firststack, where stations for unloading and loading articles from and intothe trays operate in operable positions, the trays being arranged withvertical spacers so that the trays can be stacked on top of each otherwith sufficient spacing between them, and can be raised and lowered inthe adjacent stacks by the elevating and lowering system which operateson respective bottom trays of the stacks, which picks up and depositsthe trays on the lower translation device at an appropriate time, alowering device of the elevating and lowering system transferring anempty tray from a last stack to a first stack of the kiln, a bottom trayof the last stack being held at a given height, above the lowertranslation device, by grippers which are activated and disabled in stepwith the elevating and lowering device, wherein the gripper which holdsthe lowest trays of the first and last stacks at the appropriate heightcomprise forks orthogonal to short sides of the trays, supported by ahorizontal guide which is fixed to uprights of a frame of the kiln andon which the forks can be moved longitudinally by jacks which can bringactive edges of the forks from a rest position, in which the edges areretracted from the trays, to a position of gripping the tray to be heldat the appropriate height, in which the active edges of the forks arefitted around the shanks of the spacers of the tray or under the tray.28. A vertical kiln comprising a drying chamber having two or morevertical and adjacent stacks of horizontal trays which are made to riseby steps in one stack and then to descend by steps in the other stackvia an elevating and lowering system, the trays moved along horizontaltranslatory paths by a lower translation device for the transfer fromthe top of one stack to that of the adjacent stack and for the transferfrom the end of the last stack to the start of the first stack, wherestations for unloading and loading articles from and into the traysoperate in operable positions, the trays being arranged with verticalspacers so that the trays can be stacked on top of each other withsufficient spacing between them, and can be raised and lowered in theadjacent stacks by the elevating and lowering system which operates onrespective bottom trays of the stacks, which picks up and deposits thetrays on the lower translation device at an appropriate time, a lowerdevice of the elevating and lowering system transferring an empty trayfrom the last to the first stack of the kiln, the bottom tray being heldat a given height, above the lower translation device, by grippers whichare activated and disabled in step with the elevating and loweringdevice; and an upper translation device which cyclically transfers atray from the top of one stack of trays, which has an ascendingmovement, to the top of the adjacent stack of trays, which has adescending movement, the upper translation device comprising horizontalchain conveyors located at the sides of the tops of the stacks andparallel to the short sides of the trays, the chains of each conveyorrunning around end sprockets with horizontal axes, rectilinear branchesof the chains being controlled by rectilinear guides which leave freeone side of each chain, to which are fixed carriages spaced apart withthe same distance between centers as that found between two spacerslocated on a short side of a tray, the carriages being provided withrollers which, as the carriages pass along a lower branch of theconveyor, run on a rectilinear fixed guide, and the carriages havinglevers pivoted parallel to the chains, flat ends of these levers, shapedinto horizontal hooks, projecting towards the stacks of trays, above theplan dimensions of the stacks and with the opening of the hooksorientated in the direction of translation of the trays, while theopposite end of each of the levers carries a roller which as it passesalong the rectilinear branches of the conveyor, interacts withrectilinear guides, the lower of which is grooved, double-acting, and isconnected to the elevating and lowering system, for lowering andelevating, the hook-shaped ends of the levers, respectively, thehook-shaped levers gripping the upper tray of the stack with theascending movement as the hook-shaped levers pass along the lower branchof the conveyor, by upper projecting parts of corresponding spacers,under heads of the respective spacer, after which the levers rotate toraise the gripped tray, to space the gripped tray apart from theunderlying tray and to enable the gripped tray to be translated, whileon completion of the translation, the levers rotate in the oppositedirection, to lower the translated tray and deposit the tray on theunderlying tray, after which the conveyor reverses movement to retractthe hook-shaped levers, to bring the hook-shaped levers to a position inwhich the hook-shaped levers do not interfere with the spacers of theupper trays of the stacks.
 29. A vertical kiln comprising a dryingchamber having two or more vertical and adjacent stacks of horizontaltrays which are made to rise by steps in one stack and then to descendby steps in the next stack via an elevating and lowering system, andwhich are moved along horizontal translatory paths by a lowertranslation device for the transfer from the top of one stack to that ofthe adjacent stack and for the transfer from the end of the last stackto the start of the first stack, where stations for unloading andloading articles from and into the trays operate in operable positions,the trays being arranged with vertical spacers so that the trays can bestacked on top of each other with sufficient spacing between them, andcan be raised and lowered in the adjacent stacks by the elevating andlowering system which operates on respective bottom trays of the stacks,which picks up and deposits the trays on the lower translation device atan appropriate time, a lower device of the elevating and lowering systemtransferring an empty tray from a last stack to a first stack of thekiln, the bottom tray being held at a given height, above the lowertranslation device, by grippers which are activated and disabled in stepwith the elevating and lowering system, wherein the translation deviceprovides a path for at least a limited number of trays to carry out anannular movement along a short path of a short cycle as compared with anormal path of a normal cycle whereby the limited number of trays areraised to pass into the loading station, and then raised by one or moresteps and then translated towards a final stack where the trays descendto pass into the unloading station and then descend and are translatedback into a first stack, under the loading station, for the repetitionof the short cycle; and an auxiliary means for raising and holding traysnot included in the short cycle, the auxiliary means having auxiliaryconveyors for translating the trays not included in the short cycle fromthe first stack with an ascending movement to the last stack with adescending movement.
 30. The vertical kiln according to claim 29,wherein the auxiliary means comprises forks fixed to uprights of a frameof the kiln with the interposition of a vertical guide and sliding blockunit connected to a raising and lowering actuator.
 31. The vertical kilnaccording to claim 29, wherein auxiliary conveyors provide for movementtowards and away from the stacks of trays, wherein in a normal operatingcycle of the kiln, the hook-shaped levers of the auxiliary conveyors donot interfere with normal movement of the trays.
 32. The vertical kilnaccording to claim 31, wherein the auxiliary conveyors can be used totranslate the trays between the tops of the stacks when oscillatinglevers of the auxiliary conveyors act in cavities of frames of the traysor on bases of the trays.
 33. The vertical kiln according to claim 29,wherein the auxiliary conveyors comprise rectilinear conveyors parallelto upper conveyors, the rectilinear conveyors having chains runningaround sprockets with vertical axes and with teeth, the rectilinearconveyors can carry out translation of the trays by pushing the trays,rails being provided under active branches of the upper conveyor andrectilinear conveyor and parallel to the upper conveyor and therectilinear conveyor, the rails being fixed to oscillating levers andconnected to actuators which hold the rails in a retracted position inwhich the rails do not interfere with the trays, but which can translatethe rails and insert the rails under the tray or trays to be translatedso that the rails bear on these trays and raise the trays in theappropriate way.
 34. The vertical kiln according to claim 28, furthercomprising rectilinear conveyors with movable rails which can be used inplace of the horizontal chain conveyors.
 35. The vertical kiln accordingto claim 33, wherein the auxiliary means can be made in sections withindependent movements such that the auxiliary means can provide thetranslation of the trays between lower parts of intermediate stacks of akiln having more than two adjacent stacks of trays, when the kiln isoperating with a normal cycle.